1. Technical Field
The present invention relates to a measuring device having an extended first electrode for being inserted into a material to be measured and having a sheath which at least partially surrounds the first electrode.
2. Description of Related Art
Such measuring devices are used, for example, for measuring the pH of foodstuffs such as meat, for example. Typically, a chamber is formed between the first electrode and the sheath in which a second electrode formed from a gel, for example, is installed. Both electrodes are connected to an evaluation circuit to determine the pH of a liquid of the material to be measured which has infiltrated between the electrodes.
For the measurement, the measuring device having the first electrode is pushed with great force into the material to be measured, resulting in a considerable mechanical load on the first electrode. First electrodes for pH measurement are usually made of glass, or have glass as the sheath, and can bear a high load in the axial direction and thus in the insertion direction. Perpendicular to the axial direction, these first electrodes are capable of bearing only a light load due to the brittleness of glass, which can result in breakage when a load is applied in this direction, as when the measuring device is tilted during insertion or withdrawal.
To avoid this problem, measuring devices have been provided in which the glass electrode or the gel surrounding the glass electrode is enclosed by a glass sheath and then by a metal or plastic sleeve. Although the load-bearing capacity of the glass electrode perpendicular to the axial direction does increase somewhat, the slightest deformations of the sheath, which are transmitted directly to the glass electrode, result in breakage of the first electrode and/or the glass sleeve surrounding the gel.
The double sheath made of glass and plastic also results in a larger diameter in the region of the probe tip, which during measurement creates large holes in the material to be measured.
It may be desirable to provide a measuring device having a first electrode which is more robust with respect to loads applied perpendicularly to the axial direction.